1. Technical Field
The present invention relates generally to an optical radar system which is operable to track an object present in a front detection area. More particularly, the invention relates to a laser radar system which may be employed in an automotive anti-collision system for automatically detecting the presence or absence of a preceding vehicle and measuring distance to the preceding vehicle.
2. Background Art
Japanese Utility Model First Publication Nos. 61-3485 and 613486 disclose conventional optical radar systems wherein a prism or a reflective mirror are disposed in light emitting or light receiving units for assuring a wide detection range.
In order to ensure a wide detection range without use of such a prism and/or a reflective mirror, it is necessary to widen a light-sensitive surface of a light receiving element and employ a condenser lens system having a short focal length in an optical system of the light receiving element. The widening the light-sensitive surface of the light receiving element, however, causes a parasitic capacity to be increased proportionally, resulting in a response rate of the light receiving element being undesirably reduced. In addition, the condenser lens system requires a wide light receiving area for capturing light as much as possible, causing the focal length of the condenser lens system to inevitably become long. This results in an obtainable angle of field of the radar system being restricted unadvantageously.